1. Field of the Invention
The present invention relates to an amplifier, especially a pulse power amplifier used for a pulse radar transmission system.
2. Description of the Related Art
In the technical field of pulse radar transmission systems, a pulse power amplifier is applied thereto. The pulse power amplifier includes a semiconductor element, for example, a field effect transistor (FET), for amplifying electrical power. As shown in FIG. 1, a pulse power amplifier 50 includes an FET 51, an FET 52, an FET 53, and a switching circuit 54. Additionally, the pulse power amplifier 50 includes a signal input terminal 55, a signal output terminal 56, and a pulse input terminal 57. A source signal is supplied to the signal input terminal 55. An amplified signal is transmitted to the signal output terminal 56. The FETs 51 to 53 are connected in three cascaded stages. The FETs 51, 52, and 53 have gate electrodes serving as input terminals, drain electrodes serving as output terminals, and source electrodes serving as common terminals. A voltage of a positive bias power supply 60 is switched by the switching circuit 54 in response to a modulation pulse transmitted from the pulse input terminal 57 so as to be delivered to the drain electrodes for amplifying operations. An input voltage of a negative bias power supply 61 is delivered to the gate electrodes. Then, the source signal supplied from the signal input terminal 55 is amplified by the FETs 51 to 53, and is modulated based on the modulation pulse to be transmitted as a transmission pulse. The Japanese laid open publication (Kokai) 2001-16045 discloses equalization of saturated output power so as to keep the transmission pulse constant by varying a bias voltage supplied to a drain electrode of an FET serving as a power amplifier element.